Me and my wife cross the border 5 times a week between Windsor and Detroit - tunnel or the bridge. We show them our passport, I797 and I94 as both of us live in Windsor and work in MI on H1B. We have been doing this for the past 8 months.
Few weeks ago, they handed out flyers notifying of visa requirement for Cdn PRs of commonwealth nationalities. Now they have stopped. We do not worry about it since we have a stamped visa in our passports for the past 3 months if they do ask for one. We got our visas since our company attorneys suggested to do so.
As far as questions that the border fellas ask, it varies and makes up for an interesting experience everyday. We have experienced one rude female so far among the plenty at the US and Cdn booths. So, you can see its not at all bad.
Questions we have been asked:
1. Citizenship
2. Purpose of travel
3. Status in Canada and show documentation.
4. Is "she" going to work too? (refering to my wife)
5. Anything to declare?
6. Any alcohol, tobacco, firearms, etc?
7. Is that your daughter (refering to my wife!!!!)?
8. Whose car are you driving?
9. How are you both related? (we have different last names)
10. How long were you gone? (Q from canada)
11. Where do you live?
We have been, three times to be precise, lucky winners of "Random search" at the Cdn crossing and were sent to secondary inspection for a quick search of our car. They also verified our documents on their computer. They mentioned that it happens since we are frequent travelers across the border.
I have been sent to sec insp. once at the US side since I had automotive samples and they had to check it out.
I also drive a company vehicle (with MI plates) using a Commuter's Conveyance Permit issued by the Canada customs.
We were once refused entry into Canada since my wife was driving a MI rental car. We had to go back to US, drop the car off and return with our car. That was a pain in the butt!
We usually get more questions on the US side if I drive my MI company car since they are want to know what I was doing in Canada. I, now just tell them before they ask that I am driving a business vehicle and live in Windsor.
Hope this helps.